Bacteria: Definition, Characteristics, Types

Are you curious to know about the first organism that appeared on the earth? Just for the sake of a glimpse, it was none other than “BACTERIA” that suggests life probably began around 4 billion years ago . The oldest known fossils are bacteria-like organisms. Life has evolved rapidly into a multitude of life forms over many millennia from that bacteria only. However, our ancestry back to this single-celled organism can still be traced. In this article, we are going to have a detailed analysis of that particular organism (Bacteria) that is believed to be on the earth first all.

Introduction

Definition:

Diagram of Bacteria

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History

• Pasteur and Robert Koch gave the Germ theory stating that diseases were caused by germs.
• In 1910, the scientist Paul Ehrlich announced the development of the first antibiotic Salvarsan to cure syphilis. Paul was the first to detect bacteria by using stains.
• In 2001, Joshua Lederburg coined the term “gut microbiome,” which refers to all the bacteria present in the intestine.

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Characteristics of Bacteria:

• Bacteria are single-celled (unicellular)organisms.
• They don't have organelles such as chloroplasts and mitochondria, and also true nuclei are absent in them.
• DNA is continuous and circular and is mainly located in a nucleoid.
• An irregularly shaped region i.e. nuclear membrane is not present in the nucleoid.
• Bacterial cells have a cell membrane as well as a cell wall (typically made of peptidoglycan)..
• Many bacteria need a cell wall for survival.
• Reproduction occurs through binary fission(splitting of a bacterial cell after a certain size).
• Bacteria reproduce asexually.
• Same DNA just as their parent cells is found in both daughter cells that result from binary fission.

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Types of bacteria

• Shape
• Composition of the cell wall
• Mode of respiration
• Mode of nutrition
• Temperature

Based on Shape:

Based on cell wall composition:

Based on Respiration:

Based on mode of nutrition:

• Heterotrophic bacteria :

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• Autotrophic bacteria:

Based on temperature

1. Psychrophiles:

• Bacteria that can grow between -20 degree celsius to 20 degrees.

2 . Psychrotrophs (facultative psychrophiles):

• Those bacteria that can grow even at 0°C but the optimum temperature for growth is (20-30)°C
• For Example Pseudomonas, Flavobacterium, Alcaligenes, Acinetobacter, and Bacillus

3. Mesophiles:

• Bacteria that grow at an optimum temperature 37-degree celsius are called mesophiles.
• Human pathogens are mesophilic.
• Examples : E. coli, Salmonella, Klebsiella, Staphylococci.

4. Thermophiles:

• Bacteria which grow above 45 degrees celsius are called thermophiles.
• Examples: Streptococcus thermophilus, Bacillus stearothermophilus, Thermus aquaticus.

5. Hyperthermophiles:

• Bacteria which have an optimum temperature of growth above 80 degrees celsius are called hyperthermophiles.
• Examples: Thermodesulfobacterium, Aquifex etc.

Reproduction in bacteria:

• Binary fission:

• Transfer of genetic material:

• Spores:

Useful Bacteria:

• Converting milk into curd and manufacturing enzymes which help in digesting milk and other dairy products is done by Lactobacillus or lactic acid bacteria
• Fermentation of food products is done by Streptococcus and Bacillus
• Bacteria which helps in improving the body’s immunity system are Actinobacteria, Bacteroidetes, Firmicutes and Proteobacteria
• Streptomycin and tetracycline are used in the production of antibiotics which prevent bacterial infection.
• E.coli bacteria are found in the stomachs of animals like cows, buffaloes, and other species to aid in the digesting process.
• Bacillus thuringiensis is a bacterium that can be used in agriculture instead of pesticides without harming the environment.
• Rhizobium bacteria is a useful bacteria that help break down nitrogen as plants cant take nitrogen directly so take nitrogen from the soil by nitrogen fixation.
• Anaerobic bacteria belonging to Actinomyces , Bifidobacterium , Clostridium , Propionibacterium and Peptostreptococcus genera are helpful in sewage treatment and also in cleaning oil spills.
• Wide range of bacteria are used in molecular biology, biochemistry and genetic research .

Harmful bacteria

• Strep throat: Streptococcus bacteria
• Staph infection: staphylococcus bacteria.
• Cholera: Vibrio cholerae
• Tuberculosis:Salmonella Typhi:
• Food poisoning: Clostridium botulinim
• Tetanus: Clostridium tetani .

Common Bacterial infection:

• Ear infection
• Strep throat
• Sinusitis
• Whooping cough
• Bacterial meningitis
• Urinary tract infection (UTI)
• Bacterial vaginosis (BV)
• Syphilis
• Gonorrhea
• chlamydia.

Prevention of Bacterial infection

• Proper washing of wounds.
• Timely vaccination.
• Use of surface disinfectants to kill pathogenic bacteria.
• Cooking food properly.
• Eating hygienically prepared food.
• Proper sterilization of needles and other surgical equipment.
• Washing and sanitizing hands at regular intervals.
• Avoiding unprotected sexual intercourse.
• Being mindful and avoiding public places visiting if infected.
• Avoid sharing personal items like toothbrushes, razors, soap, utensils, handkerchiefs etc.
• Staying neat and clean.